Measurement of interaction between antiprotons

Abstract

One of the primary goals of nuclear physics is to understand the force between nucleons, which is a necessary step for understanding the structure of nuclei and how nuclei interact with each other. Rutherford discovered the atomic nucleus in 1911, and the large body of knowledge about the nuclear force since acquired was derived from studies made on nucleons or nuclei. Although antinuclei up to antihelium-4 have been discovered 1 and their masses measured, we have no direct knowledge of the nuclear force between antinucleons. Here, we study antiproton pair correlations among data taken by the STAR experiment 2 at the Relativistic Heavy Ion Collider (RHIC) 3 and show that the force between two antiprotons is attractive. In addition, we report two key parameters that characterize the corresponding strong interaction: namely, the scattering length (f 0 ) and effective range (d 0 ). As direct information on the interaction between two antiprotons, one of the simplest systems of antinucleons, our result provides a fundamental ingredient for understanding the structure of more complex antinuclei and their properties.Although the theory of Quantum Chromodynamics (QCD) provides us with an understanding of the foundation of the nuclear force, this binding interaction in nuclei operates at low energy, where the force is strong and difficult to calculate directly from the theory. For that reason, a common parameterization of the effective interaction between nucleons is based on experimental measurements, and the corresponding parameterization for antinucleons remains undetermined. Ultra-relativistic nuclear collisions produce an energy density similar to that of the Universe microseconds after the Big Bang, and the high energy density creates a favourable environment for antimatter production. The abundantly produced antiprotons provide the opportunity to measure, for the first time, the parameters f 0 and d 0 of the strong nuclear force between antinucleons rather than nucleons.The technique used to probe the antiproton-antiproton interaction involves momentum correlations, and it resembles the space-time correlation technique used in Hanbury-Brown and Twiss (HBT) intensity interferometry. Since its invention for use in astronomy by Robert Hanbury-

Structural investigation of humanS. aureus-targeting antibodies that bind wall teichoic acid

“…33 This Fab was previously crystallized with the 1-phosphoribitol β-WTA analog, 33 but also crystallized in the apo form as well as with 5-phosphoribitol β-WTA (Figure 6A). The 4497 Fab crystallized in the P2 1 2 1 2 1 space group, with two equivalent molecules in the asymmetric unit (Table 1).…”

“…33 These mAbs were screened for binding to a panel of clinically relevant S. aureus strains in vitro , and for binding to the highly virulent community-acquired MRSA strain USA300 strain immediately after isolation from infected mouse kidneys. Four of the mAbs (4462, 4497, 6078, and 7578) were found to bind to wild-type S. aureus USA300 when analyzed by flow cytometry (Figure 2).…”

“…To simplify WTA to its basic components for structural interrogation, we generated a synthetic WTA mimic by chemical synthesis. 33 This minimal epitope contained the core five carbon ribitol group O-linked to GlcNAc via a β-anomeric (equatorial) bond in the 2-position. This bond arrangement was chosen based on data indicating that all three of the antibodies bind native bacteria displaying the β-O-GlcNAc form of WTA (Figure 2).…”

“…Importantly, our research showed that α-WTA was not expressed on the surface of all S. aureus isolates, whereas β-WTA was found on all isolates tested. 33 Therefore, we only sought to crystallize the β-WTA antibodies 4467, 6078, and 4497 with a synthetic WTA analog, given the potential of these antibodies as therapeutic candidates. Similar α-WTA analogs were not synthesized for crystallization with 7578 due to the lower therapeutic potential of the antibody and difficulty of the required carbohydrate chemistry.…”

“…Antibodies specific for S. aureus WTA conjugated to a highly potent rifampicin analog have been shown to have potent bactericidal activity against MRSA in preclinical models of infection. 33 Here, we structurally characterized three WTA-reactive antibodies from this antibody-antibiotic conjugate (AAC) program that were cloned from a patient recovering from S. aureus infection. We show that each of the three antibodies is specific for the WTA phosphoribitol repeating unit containing a β-linked GlcNAc at the C2 position.…”